三峡库区典型流域水质时空特征及污染防控策略

    Spatio-temporal characteristics of water quality and pollution prevention strategies in typical watersheds in the Three Gorges reservoir areas

    • 摘要: 为了解三峡库区典型小流域不同土地利用类型下水质的变化特征,于2015-2020年对三峡库区长坪小流域开展水质监测,对不同土地利用类型下水体中的总氮(Total Nitrogen,TN)、硝态氮(NO3--N)、氨氮(NH4+-N)、总磷(Total Phosphorus,TP)、可溶态总磷(Dissolved Total Phosphorus,DTP)和颗粒态总磷(Particulate Phosphorus,PP)浓度的时空变化规律进行研究,识别流域内主要氮磷污染源,从而提出针对性的污染防控策略。结果表明:1)不同土地利用类型氮磷输出浓度从大到小依次为村庄、坡耕地、林地和水库,其TN平均浓度分别为8.29、2.88、1.57和1.43 mg/L,TP平均浓度分别为0.25、0.13、0.09和0.07 mg/L。2)不同土地利用类型的水质在汛期和非汛期存在差异,村庄氮磷输出浓度为非汛期高于汛期,坡耕地、林地和水库则表现为汛期高于非汛期。3)内梅罗综合污染指数评价结果表明林地和水库的污染程度均为清洁水平,坡耕地污染程度为轻污染水平,村庄受散养生猪数量的影响,污染程度从污染水平转变为重污染水平。4)长坪小流域TN和TP年输出负荷总量分别为4 278.59和364.93 kg/a。畜禽养殖源是小流域氮磷最主要的污染源,其TN和TP的输出负荷分别占流域总负荷的45.69%和71.77%。坡耕地的TN和TP单位面积污染负荷分别是村庄的7.58%和1.79%,与村庄相比,坡耕地具有显著的低污染特征,因此,以坡耕地消纳村庄污水和畜禽粪便,可促进流域内粪污的就地消纳,达到多源共治的效果。基于小流域不同土地利用类型的水质特征和生态系统服务功能,将流域划分为林草水源涵养区、村庄污染控制区和坡耕地水土保持区,并进行分区协同防控,促进流域农业面源污染系统高效治理。

       

      Abstract: Water quality has been greatly confined to the nitrogen loss and phosphorus pollutants caused by agricultural production in the Three Gorges Reservoir Area. This study aims to clarify the characteristics of water quality under different land use types in typical small watersheds. The water quality monitoring was conducted in the Changping small watershed in the Three Gorges Reservoir Area from 2015 to 2020. A systematic investigation was made on the change patterns of Total Nitrogen (TN), nitrate nitrogen (NO3--N), ammonia nitrogen (NH4+-N), Total Phosphorus (TP), Dissolved Total Phosphorus (DTP), and Total Particulate Phosphorus (PP) concentrations in the water bodies under land use types, together with their influencing factors. The results showed that: 1) The overall nitrogen and phosphorus output concentrations of land use types were ranked in the order of the village > sloping farmland > forest land > reservoir. The average TN concentrations were 8.29, 2.88, 1.57, and 1.43 mg/L in the villages, sloping farmland, forest land, and reservoirs, respectively. The average TP concentrations were 0.25, 0.13, 0.09, and 0.07 mg/L, respectively. 2) There was a different water quality of land use types during the flood and non-flood periods. The concentration of nitrogen and phosphorus output in the villages was higher in the non-flood period than that in the flood period. The sloping farmland, forest land, and reservoirs showed a higher concentration in the flood period than those in the non-flood period. 3) The Nemerow comprehensive pollution index demonstrated that the pollution level of both forest land and reservoir was at the clean level, and the sloping farmland was at the light pollution level. But, the pollution level of the village deteriorated from the pollution level to a heavy pollution level, due to the increase in pig farming. 4) The annual output loads of TN and TP in the Changping sub-basin were 4 278.59 and 364.93 kg/a , respectively. Livestock and poultry breeding was the most important source of nitrogen and phosphorus pollution in the sub-basin, with the output loads of TN and TP accounting for 45.69% and 71.77%, respectively. The TN and TP pollution load per unit area of sloping land in the sub-basin were 7.58% and 1.79% of those of village, respectively. The sloping farmland presented significantly low pollution characteristics, compared with the village. Therefore, the sloping farmland can be used to absorb the village sewage and livestock manure, in order to promote the local absorption of manure in the basin for the better effect of multi-source co-management. The land use structure of the whole watershed can also be adjusted in an effective way to control agricultural surface pollution. Therefore, the small watershed was divided into the forest and grass water connotation zone, village pollution control zone, as well as sloping farmland soil and water conservation zone, according to the water quality and ecosystem service function of land use types. Zoning collaborative prevention and control strategy should be an effective way of promoting the water resource, nitrogen and phosphorus transfer from one pollution control zone to another pollution control zone in order to preventing the pollutants export to the out of the small watershed. The finding can provide the theoretical basis and technical support for the control of nitrogen and phosphorus pollution in the protection of water sources in the Three Gorges Reservoir Area.

       

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